Process for roasting of sulfide ores



July 2, 1957 A. A. J. QUINTIN 2,797,987

PROCESS FOR ROASTING 0F SULFIDE ORES Filed Feb. 26. 1954 PRIOR ARTINVENTOR I MPH-11.11 [IL-Mira 341N 09 PRGESS FOR .RDASTING OF SULFI DEORES" Albert Andrel'osepli Quintin, Overpelt, Belgium, assignor toCompagnie des Metaux dOverpelt-Lommel et de Corphalie,Overpelt-lez-Neerpelt; Belgium, a- Belgian body corporate ApplicationFebruaryl, 1954,.Serial No. 412,892

4 'GliiimS. (Cl; 759) This invention-relates to a process for' roastingsulfide TSl- I It is-ltn'own'to' roast sulfide ores-by a process ofsemi'- suspension, or fluidiza'tion, of the ore: in a current of air oroxidizing gas; the ore may be in the form of nat-. ural grains; orthesegrains; may havezbeentmanufactured by; any method of sintering; and.granulation; or theme may-beintheform of a-fine powder: Useis: made forthe'roasting of an.enclosure-which generally has a" height which is'greater than; its width, and at: the lower part of. which at perforateddiaphragm" is-- provided, through which air or'ant oxidizing; gas isblown; Afterv theen-z closurehasbeen heated tothe. temperature ofreaction, raw-ore'issfed above the diaphragm andthe amount of oxidizing.gas orair admitted through the. diaphragmis regulatedsothat its speedimmediately. above the dia-. phragm shallbe sufficientr to place theorein arstate of. semiasuspension. and agitation generally calledfluidiza tion similar tothatof. boiling water, but insufficient. tocarry. over. the major part of the ore outside the roasting enclosure.

The ore which accumulates in the roasting enclosureor furnace isremoved, in a continuous or discontinuous manner, generally by overflow,through suitable outlets provided for thatpurpose in the side wall ofthe enclosure.v

In the accompanying. drawings,. Figure 1 shows diagrammatically"a knowndevice for carrying out a process" of" the above kind. In Figure 1,,the'referencenw meral 1 showsthe roasting enclosure, 2' is'theperforated diaphragm; 3 is a wind box which is fed -by airor'oxidizinggas under pressure through an' orifice' ll Theoverflow of the ore takes"place through-an orifice 5 and through a pipe 6 intoahopper 7"havingatight jointfit from which it can'be removed by means of adamper 8, Thereference numeral 9" shows an outlet forrthe roasting gases; 10"is apipe for feeding=rawore into the enclosure, theorebeing fed by a screw11 from a hopper 12'l The screw 11" is driven by a motor 13-.

The above system has two important drawbacks; when applied to ore in theform of grains:

(1) The removed material represents practically? an average sampling ofthe material which is fluidized in the enclosure 1'. Itcontains acertain proportion of grains whichhave remained too short a time insidethe enclosure to be completely desulfurized.

(2') The speed of the oxidizing gas or air blown through the diaphragm 2must be chosen so asto maintain the larger grains in. suspension and toavoid the carrying over of smaller grains as. much as possible. Thisrequires a very precise sizing of the grains, thus limiting .withinnarrow limits the difierence in-size between the largest. grain andthesmallest grain if it is desired. to avoid either a. carrying over of toolarge quantities. of materials together with the oxidizing gas throughthe orifice 9, oran accumulation of the larger grains at the lower partof the-roasting enclosure where they would be insufliciently roastedowing to their. lack of mobility.

rates Patent The present invention has for its obpject to avoid theabove drawbacks.

With this object in view, the invention consists in a process for theroasting of sulfide ores in which the roasting is mainly carried out ina state of fluidization, that is in a state of. semi-suspension of themass of ore, by means of a current. offair or oxidizing gas (hereinaftercalled sometimes oxidizing gas alone or air alone) andi'n sucha'processdividing the amount of oxidizing gasnecessary'for the roastinginto various portions,.infooting the said portions at various points ofthe mass of the ore subjected'to-roasting to produce an intermediatezone of intense turbulence of the OIC"WhlCl'1 separates anupper zone in'which theore is fluidized, that is in which ore isin a state ofsemi-suspension, and a lower zonein which the grains'of'ore are at restrelatively to each other; causing the mass of ore in which the grainsare" at rest relatively to each other toadvance downwards=ina regularmanner by gravity, removing substantia'llytherentire' m'ass of roastedore at the lower part of ther'roastingxenclosure; ands causing a slowcurrent of air on of: oxidizingrgas to passthroughthe mass of ore inwhich: the grains: are 'at' rest relatively to each other'fo'rcompleting: the; roasting. of the grains without agitating them;

The air or gas required for completing-the: roasting operation, iscaused totpass' in acountercurrent direction through-theiroastedtmaterial of the zone where. the grains are comparatively at restrelatively to each other.

Theintermediate zoneof. intenseturbulence may consist" of. a. pluralityof convergent-divergent. spaces into which air or. oxidizing gasrisblown.

Theinjection chair. or oxidizing gasintothesaid: intermediate. zone. maybe efiected. by means of perforated hollow bars immersed. into. the.mass. of ore and having a shape such asto-offer. aminimum section of.passage to the ore at approximately, the level wherethe main blowing ofair. or oxidizing, gas takes place. The main portion of air or.oxidizing gas-(primary air) is blown at high speed, for instance 15 to30 meters peresecond, through the holes of the bars so. that thematerial shall be maintained at that. level. between the bars in a stateoffluidization withviolent whirling or turbulence. A secondary and muchsmaller amount of air oroxidizing gas (secondary air) is blownintothemass of meat a lower level of the bars, in" the zone of relativerest where there areno movements of'the grains relatively-to eachother.

According to another characteristic feature of the invention, anothersmall amount of air or oxidizing gas (tertiary air) is injectedjustabove the level of theout let of'ore from the lower part of the roastingenclosure.

The total amount of secondary'plus tertiary air'iscarefully chosensmallenough so-that it does not agitate the grains relatively to each otherin the zone' of" relative rest that extends from about" the level of theprimary injection to" the outlet ofthe roasted are.

The secondary" air, assisted' by'the' tertiary air; has for its'main'obiect, to complete the combustion of the" sulfur inflsulfidetorm,before the'mass of material=has been appreciably cooled. The: tertiaryair fiowingina countercurrent:direction'has for its firstobject-torecover: the heat of the "roasted oreand tobring' it'into thereaction zone,- whilstpreventing the formation of. sulfates.

The-hollow bars for theinjection of primary and'sec ondary air-may havea cross-section formed of two tr-iangles joined by their: bases; I

Fig. Zin-the a'ccompanyingdrawings shows-in-elevationdiagrammaticallyand by" way ofexample: one mode of carrying:theinvention into= effect, which-has been. applied in practicetotheroasting of raw blende: (impure zinc sulfide.) which originally was he afinelyr dividec lr state, and which was granulated by a suitable processand sized, for instance between /2 mm. and 4 mm., prior to its beingroasted.

In Figure 2, the reference numeral 1 shows the furnace enclosure, 2 arehollow bars, made of a material which is fire-resistant and preferablygood conductor of heat, for instance of stainless steel.

The bars 2 have two independent chambers, an upper chamber 3 from whichair or gas passes through nozzles 4, and a lower chamber 5 from whichair or gas passes through nozzles or slots 6. All the chambers 3 areconnected with a feeding pipe (not shown) for primary air underpressure. All the chambers 5 are connected with a second feeding pipe(not shown) for secondary air, also under pressure. 7 is a hopper, whichpreferably is heat-insulated. 8, 8 are wind boxes which feed nozzles orslots 9. They are connected with a third feeding pipe (not shown) fortertiary air, also under pressure.

10 is a feeding screw driven by a motor 11 with a change speed gear,which screw removes roasted material to an extent such as to maintainthe material in state of semisuspension up to a constant level 17 insidethe upper part of the reaction enclosure. 12 is a hopper with a tightjoint fit in which roasted material accumulates. 13 is a hoppercontaining raw material, 14 is a feeding screw driven by a motor 18having a change speed gear. 15 is a pipe for feeding raw material intothe reaction enclosure, preferably made of stainless metal. 16 is anorifice for the escape of roasting gases.

As shown in the drawing, the whole of the tertiary, secondary andprimary air passes through the fluidized material above the nozzles 4,4. The total amount of air is so chosen as to obtain, in the section ofthe furnace extending from above the hollow bars 2, 2 up to the level17, a speed which at the roasting temperature (950 to 1050 C. forblende) will maintain the material in a state of fluidization withmoderate whirling. The said speed, calculated for cold air and for anempty furnace, is of the order of 50 cm. per second. The primary air,injected under pressure into the chambers 3 of the bars 2, representsabout 80% of the total amount of air.. The nozzles 4, which are spacedat regular intervals along the bars, have orifices of a size such thatthe escaping air has a speed of the order of 15 to 30 metres per second(calculated with regard to cold air). The bars 2 have a double prismaticshape, upwards and downwards from the nozzles 4, so that the minimumpassage section for the ore between the bars is located at or about thelevel of the nozzles 4. This minimum section represents about 50 to 70%of the total horizontal section of the furnace at the level 17. Thedistance between the primary nozzles 4 and the secondary nozzles orslots 6 is about 30 to 50 cm. The amount of air injected through thenozzles or slots 6 is about 10 to 15% of the total air. The amount ofair injected through the nozzles or slots 9 is of the order of 10 to 5%of the total air. The nozzles or slots 6 and 9 have a sufiiciently largesection to impart a small speed to the outflowing air, for instanceabout 5 metres per second, so as not appreciably to disturb the state ofrelative rest of the grains inside the lower part of the enclosure.

It follows that below the level of the nozzles 4, the speed of the airis considerably lower than that which would be required to produce aturbulence in the material. This speed, calculated for cold air and thehorizontal section of the furnace supposed empty does not exceed some 10cm. per second. The grains of material therefore remain at restrelatively to each other, and the mass of grains goes downwards bygravity in a regular manner between the bars and through the hopper 7according as the removal of roasted material by means of the feedingscrew 10 proceeds, the movement of latter screw being regulated so as toremove the amount of roasted blende or other ore corresponding to theamount of raw blende or other ore which is fed by the screw 14. Itfollows that the small amount of sulfur in the state of sulfide which isstill contained in certain grains at the level of the nozzles 4 issystematically burned by the two countercurrent air currents injectedthrough the nozzles 6 and 9, the first current being heated by the heatrecovered from the roasted ore in the hopper 7, the second current beingheated by conductivity from the walls of the chambers 5. It may also beuseful, but not indispensable, to preheat the air in any suitable mannerbefore it enters the chambers 5, for instance by a heat exchange withthe roasting gases which leave at 16.

A complete roasting can thus be obtained. The percentage of sulfur insulfide form is reduced to less than 0.05% and the percentage of sulfurin sulfate form is practically equal to the amount of sulfur alreadycombined with calcium and with barium in the form of fixed sulfates;moreover, there is no re-formation of zinc sulfate, below the level ofthe nozzles 4, since the combustion of the small amount of sulfideremaining in the material is effected above 900 C., after which thesubsequent cooling takes place in a current of pure air, free from S02and S03.

On the other side, the gas or air passing through the nozzles 4 into agreatly reduced section of the furnace gives a largely increased airspeed per unit of cross-section. Moreover, there is a state of intenseturbulence in that part due to the opposed nozzles which blow air or gasat a high speed. It follows that the larger grains are all lifted by therapid current and are completely roasted without injecting an amount ofair which would lead to a high vertical velocity in the section of thefurnace above the bars, which would carry over too large quantities ofmaterial through the outlet 16. The practice has shown that it ispossible under the above conditions to obtain that and more of theroasted material is removed at the lower part of the reaction enclosure,less than 5% of the material being carried over with the roasting gases,because in a very fine state.

I claim:

1. An apparatus for the roasting of sulfide ore in grain form,comprising an enclosure the upper part of which has a conical shape withthe smaller section situated below, means for the admission of the oreand means for the removal of gases at the upper part of said enclosure,the upper part being followed by a cylindrical part at about the lowerend of which a plurality of hollow bars are arranged, each having asection resembling two triangles joined by their bases and provided withmeans for the injection of air from the hollow bars into the spacecomprised between the latter, the said cylindrical portion beingfollowed by a part of truncated conical shape with the smaller sectionsituated below, means being provided at the lower part of the lattertruncated conical part for the injection of air, and means for theremoval of ore at the lower part of the enclosure, as set forth.

2. In a process for the roasting of sulfide ores, the steps comprisingadmitting the sulfide ore in grain form at the upper part of a verticalenclosure, causing the sulfide ore to move downwards in the saidenclosure for a substantial portion of the height of the verticalenclosure in a continuous manner in a state of quiet fluidization in acurrent of oxidizing gases, mechanically supporting the grains at aplurality of points throughout the cross-section of the said enclosure,injecting an oxidizing gas through the grains of ore at the said pointsof mechanical support to create a zone of intense turbulence whileleaving at the points where the oxidizing gas is injected a plurality ofsubstantially vertical passages for the grains moving downwards, thenallowing the grains to move in a downward direction in a defluidizednon-expanded condition and therefore in a state of practical immobilityrelatively to each other, and removing the grains in a practicallycompletely oxidized state, at the lower end of the said verticalenclosure.

3. In a process for the roasting of blende in grain form, the stepscomprising admitting the blende at the upper part of an enclosure,causing it to move downward in a continuous manner for a substantialportion of the height of the vertical enclosure causing air to moveupwards through the grains in the upper part of the enclosure with aspeed of the order of 50 cm. per second (calculated for cold air and foran empty space), thus causing the grains in the upper part of enclosureto move in a state of quiet fluidization, mechanically supporting thegrains at a plurality of points throughout the cross-section of theenclosure, then injecting air at the said supporting points with a speedof the order of to 30 metres per second (calculated with regard to coldair) to produce a zone of intense turbulence while leaving at the pointswhere the air is injected a plurality of substantially vertical passagesfor the grains moving downwards, causing a current of oxidizing gas ofslow velocity to pass in an upward direction through the grains in thelower part of the enclosure while leaving the grains in a defluidizednon-expanded condition and therefore in a state of practical immobilityrelatively to each other, and removing the grains, in a practicallycompletely oxidized state, at the lower part of the said enclosure.

4. In a process for the roasting of blende in grain form, the stepscomprising admitting the blende at the upper part of a verticalenclosure and causing it to move downwards in a continuous manner for asubstantial portion of the height of the vertical enclosure in acontinuous manner, causing air to move upwards through the grains in theupper part of the said enclosure with a speed of the order of cm. persecond (calculated for cold air and for an empty space), thenrestricting the section of passage of the grains in the enclosure bymeans of a plurality of mechanical points of support throughout thecross-section of the enclosure with formation of a plurality ofsubstantially vertical passages and injecting air into the latterpassages with a speed of the order of 15 to 30 metres per second(calculated with regard to cold air) to produce a zone of intenseturbulence therein, while allowing the grains of ore to move downwardsin a plurality of substantially parallel streams, causing a current ofoxidizing gas of slow velocity representing 5 to 15% of the total air topass in an upward direction through the grains in the lower part of theenclosure underneath the mechanical points of support while leaving thegrains in a defluidized non-expanded condition and removing the grainsin a practically completely oxidized state at the lower part of the saidenclosure.

References Cited in the file of this patent UNITED STATES PATENTS1,885,998 Edholm Nov. 1, 1932 2,386,670 Evans 1 Oct. 9, 1945 2,465,410White Mar. 29, 1949 2,560,175 Kalbach July 10, 1951 2,612,438 MurphreeSept. 30, 1952 2,621,118 Cyr et a1 Dec. 9, 1952 2,665,899 Fassotte Ian.12, 1954 FOREIGN PATENTS 519,869 Belgium May 30, 1953

1. AN APPARATUS FOR THE ROASTING OF SULFIDE ORE IN GRAIN FORM,COMPRISING AN ENCLOSURE THE UPPER PART OF WHICH HAS A CONICAL SHAPE WITHTHE SMALLER SECTION SITUATED BELOW, MEANS FOR THE ADMISSION OF THE OREAND MEANS FOR THE REMOVAL OF GASES AT THE UPPER PART OF SAID ENCLOSURETHE UPPER PART BEING FOLLOWED BY A CYLINDRICAL PART AT ABOUT THE LOWEREND OF WHICH A PLURALITY OF HOLLOW BARS ARE ARRANGED, EACH HAVING ASECTION RESEMBLING TWO TRIANGLES JOINED BY THEIR BASES AND PROVIDED WITHMEANS FOR THE INJECTION OF AIR FROM THE HOLLOW BARS INTO THE SPACECOMPRISED BETWEEN THE LATTER, THE SAID CYLINDRICAL PORTION BEINGFOLLOWED BY A PART OF TRUNCATED CONICAL SHAPE WITH THE SMALLER SECTIONSITUATED BELOW, MEANS BEING PROVIDED AT THE LOWER PART OF THE LATTERTRUNCATED CONICAL PART FOR